Method of treating metal articles



Patented July 24, 1928.

UNITED- STATES- PATENT OFFICE;

LOUIS SCHULTE, OF PITTSBURGH, PENNSYLVANIA, ASSIGNOR T0 ALLEGHENY STEEL COMPANY, A CORPORATION OF PENNSYLVANIA.

METHOD OF TREATING METAL ARTICLES. I

No Drawing.

This invention relatcsto the manufacture of articles such, for example, as sheets, shapes or the like, from iromimn iron alloys and more particularly to tli e finishing of the surfaces of such articles.

Articles made from high chromium iron alloys (I refer particularly to those alloys having a chromium content somewhere between 8% and 60%) if annealed, or heat treated attain a hard tenacious coating resembling a'dense scale which is extremely difiicult to remove for the reason that it will not yield to acid pickling nor can it be removed satisfactorily by dry scrubbing.

An objectlof this invention is to provide .a method of treatin the surfaces of metallic articles so as to qulckly and effectively remove scale and oxide therefrom.

A further object is to provide a method of treating the surfaces of articles made from chromium iron alloys which have been heat 1 treated so as'to clean the same and simultaneou'sly provide a satin or semi-lustrous finish.

I have discovered, after many trials, that the tenacious coating on the surface of a chromium iron alloy article can be removed if suclf surfaces are simultaneously subjected to a vigorous scrubbing or scouring action and to a nitric acid bath or solution. Such a procedure not only cleans the surfaces of chromium iron or chromium steel having small perforations in its walls and which is revolved in or partly submerged in atank or bath containing a nitric acid solution. Any closed tumbling barrel may, however, be used if provision is made for a vent pipe or air valve to allow any possible hydrogen gas to escape. The commercial oblique barrel Application filed April 20, 1926. Serial No. 103,375.

revolving on a de ree angle may be used for all kinds of sma articles, especially if the container is made from chronnum 11011 or some other substance which is harder than.

the surface of the articles being treated. For example, hardened chromium iron shot,

chromium iron punchings of various sizes.

I have also obtained satisfactory results by using small river stones or pebbles where a high finish is not required, and glass balls can also be used, but hardened chromium iron or chromium steel particles are the best for all purposes and are practically indestructible.

A satisfactory acid bath. can be made of from one to ten per cent solution of nitric acid which may be either cold or warm. Heating the acid will shorten the process and produce a whiter finish.

W rat I claim as new and desire to secure by Letters Patent is 1. The method of treating the surfaces of articles made from chromium iron alloys which consists in subjecting said surfaces to the frictional action of solid particles in the presence of a nitric acid solution.

preferably screened, is satisfactory as is also 2. The method of treating the surfaces of frictional action of solid particles in the presence of a nitric acid solution.

In testimony whereof, I have hereunto subscribed my name this 17th day of April LOUIS SCHULTE. 

